One of the problems confronting the transit industry is the curving performance of the powered conventional urban heavy rapid rail truck. Among the curving performance problems are the high rate of wheel flange wear and rail gauge wear associated with operating heavy rapid rail cars on sharp curves. An additional problem that may be even more objectionable than the high wear rate is the high pitch screech or squeal that is associated with negotiating sharp curves (usually greater than 8 degrees curvature or approximately 700 feet radius).
The squeal noise and most of the wheel flange wear and rail gauge wear experienced with conventional parallel axle trucks are due to the non-radial running position of the leading axle in sharp curves. The non-radial running position results in a tracking error or an angle of attack between the wheel and rail. It is the associated wheel/rail angle of attack and lateral motion (creep) that cause noise, wear, and an unnecessarily high lateral force between the wheel flange and the rail. In addition, in the non-radial running position, there is a substantial rubbing velocity between the rail and the flange which causes additional noise and wear.
The noise problem can be mitigated by using resilient wheels, various other noise suppression measures, and by lubricating the wheel/rail interface. Of course, resilient wheels or noise barriers do not relieve the wear problem and lubrication must be very carefully controlled or there will be an increase in the incidence of flat wheels due to wheel slide during braking.
The addition of steering, however, cures the problem at the source by eliminating the tracking error and the associated wheel/rail lateral motion. The vibration which causes the noise is not generated. Flange forces are lower and the rubbing action is eliminated. With the need for wheel/rail lubrication removed, traction and braking performance become more consistent.
The anticipated benefits from the use of steerable trucks on urban transit vehicles are: reduced wheel flange wear, reduced rail gauge wear, reduced wheel/rail noise, and reduced energy consumption during curve negotiation. Where cars accumulate a high percentage of their mileage on curved track, the potential dollar savings on wheel and track wear could be quite substantial.
So called steering arms have been used to steer trucks. The steering arm concept can have two modes of operation which are known as self-steering and forced (positive) steering. In the self-steering mode, the steering input comes exclusively from the self-centering action of a tapered wheelset. The steering forces are generated by the creep forces developed at the wheel/rail contact patch. Therefore, the self-steering input is a direct function of the adhesion limits and contact geometry. In the forced-steering mode, the steering input comes from a linkage arrangement that responds to truck swivel with respect to the car body during curve negotiation. The linkage geometry positions the axles radially when the car is in a curve. Self-steering action is also present and actually aids the positive steering mode. The present invention is related to forced steering trucks.
Forced steering trucks have been used in the past. For example, patents have been issued to List U.S. Pat. Nos. 3,789,770 and 4,131,069 relating to steering trucks in railway cars.
List utilizes a steering arm at a predetermined set position dependent upon wheel base and distance between trucks to keep the wheel radial with the track. However, in some cases it may be desirable to provide oversteering or understeering. For example, by creating angles of attack between wheel flange and the track, forces are created which tend to bring the wheel flange away from the track. For example, it may be desirable to oversteer where sharp turns are involved, and understeer when high speeds are involved. Thus, it is desirable to be able to view the route of a proposed railway car to determine the overall ride conditions involving speeds and turns and then be able to design the trucks to accommodate the conditions involved, e.g., provide forced steering where the wheels of the truck move radially with the tracks or provide oversteering or understeering.
Another situation which should be recognized is that there are thousands of railway cars in existence which have little or no steering and which are likely to remain in use for many years. Because the trucks are of fixed designs to accommodate the structures of the car bodies and most generally carry many of the items, such as motors and gear boxes needed to propel the car, generally a complete redesign would normally be required to retrofit existing trucks with forced steering.
It is desirable to be able to retrofit or design forced steering trucks while at the same time utilize many of the components for driving the cars, as well as accommodating the standard designs in cars which have proven satisfactory over long periods of time. One type of railway truck involving conventional side frames, bolsters and other elements found in conventional railway cars is described in a patent to Dean U.S. Pat. No. 2,908,230.